1. Field of the Invention
The present invention relates to a fishline tension measuring device for use in a fishing reel.
2. Description of the Prior Art
The present inventor has previously disclosed, by Japanese Utility Model Kokoku Publication No. Sho. 64-5493, a fishline tension measuring device for use in a fishing reel, which is capable of measuring the tension of a fishline when fish is caught on a bait on the fishline.
FIGS. 13 to 16 show the prior art fishline tension measuring device. In these figures, reference numeral 1 designates a spool shaft rotatably supported by two side plates 5 and 7 through bearings (one bearing 3 is shown in the drawings). A spool 11 with a fishline 9 wound thereround is mounted on the spool shaft 1 so that the spool is relatively swingable and rotatable relative to the spool shaft 1. A gear train for driving the spool 1 is accommodated within and supported by the side plate 7, through which the rotational operation of the handle 13 causes the spool 1 to be rotationally driven.
The bearing 3, which supports one end of the spool shaft 1 on the side plate 5, is fitted in a ring-shaped support member 15 coaxially and integrally therewith. The support member 15 is fitted through an elastic space member 17 such as a Teflon sheet into a seat part 19 which is formed at a central and internal portion of the side plate 5. The elastic space member 17 permits the support member 15 with the bearing 3 to slightly move in the diametrical direction (i.e. the tensile direction on the fishline 9) depending on the load given to the spool shaft 1 when fish is caught on the fishline 9 and tension is applied to the fishline 9.
The support member 15 includes on the outer peripheral wall thereof a projecting portion 21 projecting from the support member 15 in a directions opposite to the tensile direction of the fishline 9 (the tensile direction being indicated by an arrow A in FIG. 15). One end of a strip-shaped strain plate 23 is screwed to the projecting portion 21. The strip-shaped strain plates 2 is formed of an SUS material or the like and has a thickness of 0.3 mm. A block 24 is fixedly secured to the other end of the strain plate 23. A tensioning screw 27 is threadingly engaged with the block 25. The tensioning screw 27 penetrates the side plate 5 in the diametrical direction thereof and supported thereby. Therefore, by screwing the screw 27 into the block 25, a given tensile force can be applied to the strain plate 23.
On the front and back surfaces of the strain plate 23, there are bonded two pairs of strain gauges 29, 31, 33 and 35, respectively. These strain gauges 29, 31, 33 and 35 are respectively used to detect the tensile force applied onto the fishline 9. In other words, when a load is applied to the spool shaft 1 due to the tensile force of the fishline 9 and thus the strain plate 23 is strained according to the load, the resistance values of the strain gauges 29, 31, 33 and 35 are changed according to the quantity of strain of the strain plate 23 to thereby detect the tensile force applied to the fishline 9.
The above-mentioned strain gauges 29, 31, 33 and 35 are connected to one another in such a bridge manner as shown in FIG. 16. In this bridge connection, one pair of mutually opposing connecting points P.sub.1 and P.sub.2 are respectively connected to a DC source, while the other pair of mutually opposing connecting points P.sub.3 and P.sub.4 are respectively connected to the inputs of a voltage amplifier 37. The output of the voltage amplifier 37 is connected to a tension display part 39.
As the conventional fishline tension measuring device is structured in the above-mentioned manner, if a fish is caught in a bait on the fishline to apply tension to the fishline 9, the tension is applied through the spool 11 and spool shaft 1 to the bearing 3 and at the same time the tension pulls the support member 15 including the bearing 3 in the direction of an arrow A shown in FIG. 15. Consequently, the support member 15, while compressing the space member 17, is slightly moved in the same direction according to the tension, which causes the strain plate 23 to extend elastically and produce strain in the strain plate 23.
Thus, when strain is produced in the strain plate 23 in this manner, the resistance values of the strain gauges 29, 31, 33 and 35 respectively bonded to the strain plate 23 are caused to vary, with the result that the balanced condition on the bridge is destroyed to thereby generate a potential difference between the connecting points P.sub.3 and P.sub.4. The potential difference is proportional to the tension to be applied to the fishline 9.
After amplified by the voltage amplifier 37, the potential difference is output to the tension display part 39, where the tension is displayed.
Therefore, if an angler views the display state of the tension display part 39, then the angler is able to judge easily the condition of the current tension.
In the above-mentioned conventional tension measuring device, however, there are still found problems to be solved: that is, since the strain plate 23 is screwed between the side plate 5 and support member 15, the structure thereof is complicated, which makes it difficult to assemble the device into a fishing reel and also increases the manufacturing cost of the device.
Further, if an operator accidentally drops down the reel or hits the reel against the rock and thus applies an external force to the reel, the thin strain plate 23 may be curved by the shock or the screwed portion of the strain plate 23 may be damaged. The original tension set for the strain plate 23 may thus be undesirably varied. For these reasons, the conventional tension measuring device is insufficient in anti-shock property.